Control circuit for automatic positioning of pairs of electrodes in smelting furnaces



JulyZl, 1970 E. c. K. svENDsEN 3,520,973

CONTRL CIRCUIT FOR AUTOMATIC POSITIONING OF PAIRS OF ELECTRQDES IN SMELTING FURNACES Filed Feb. 5. 1969 HOIST INVENIOR. Elvmn CHRISTIAN KRGER svENDsEN CONSTANT REFERENCE VOLTAGE BY l ATTORNEYS United States Patent O 3,520,978 CONTROL CIRCUIT FOR AUTOMATIC POSITION- ING OF PAIRS F ELECTRODES IN SMELTING FURNACES Eivind Christian Krger Svendsen, Oslo, Norway, assignor to Elektrokemisk A/S, a corporation of Norway Filed Feb. 5, 1969, Ser. No. 796,769 Claims priority, applicatzigr/lNorway, Feb. 10, 1968, 8

Int. Cl. H05b 7/12 U.S. Cl. 13-13 5 Claims ABSTRACT OF THE DISCLOSURE A control circuit which will adjust the position of pairs of series-connected electrodes or of either one of the electrodes in each pair, including a first differential relay for controlling the direction of movement of the electrodes and a second differential relay which determines whether the position of both electrodes or of a single electrode of the pair is to be adjusted.

The present invention relates to controls for automatically positioning pairs of electrodes which are seriesconnected to either several single-phase transformers or to one multi-phase transformer. Specifically, pairs of electrodes are series-connected within each single-phase system or sub-system, with a single regulator serving to control the position of each electrode of each pair so as to control the current through the smelting furnace.

In the past, control of electrode positions in smelting furnaces usually required a regulator for each individual electrode, which regulated according to constant impedance by measuring the potential between each electrode an-d the furnace bottom. Regulation based on constant furnace current has heretofore not been utilized in multielectrode smelting furnaces in which pairs of electrodes are connected in series within each single-phase system or sub-system. With such an arrangement, current could remain constant although there might be a wide divergence in the positions of the series-connected electrodes, i.e., the degree of immersion of one electrode in the furnace charge may result in a very high effective resistance between the electrode and the furnace bottom, while the degree of immersion of the other electrode may be such that a very low effective resistance exists between the electrode and the furnace bottom.

The present invention is directed toward preventing such a disparity between the degrees of immersion of pairs of series-connected electrodes. This is accomplished by comparing the potentials between the furnace bottom and each electrode and actuating a differential relay in response to a sufficiently large difference between these two potentials. The differential relay thus actuated controls the electrode hoist mechanism and causes this mechanism to adjust the position of only one electrode so as to maintain a substantially equal degree of immersion of each electrode of the p-air within a predetermined range. A. second differential relay responds to differences between the current in the primary winding of the furnace transformer and the voltage across the secondary winding to determine the direction in which the electrodes or the selected electrode must be moved.

A better understanding of the presenting invention may ice be had with reference to the accompanying drawing, of which:

FIG. 1 is a schematic diagram of a control circuit embodying the present invention; and

FIG. 2 is a schematic diagram of an electromagnetic hoist.

In FIG. l, electrodes 1 and 2 are inserted into a furnace 4 so as to be partially immersed in a charge 6. Below the charge is a melt 8 which is formed electrothermically as a result of current flowing between electrodes 1 and 2 and the furnace bottom 10. Power transformer 12 has its adjustable primary winding 14 connected to a suitable source of power. The secondary winding 16 of power transformer 12 has its first and second terminals connected to the upper ends of electrodes y1 and 2, respectively. The potentials between electrodes 1 and 2 and the furnace bottom 10 are impressed across the coils 18 and 20, respectively, of differential relay 22, which also includes ganged armatures 24 and 26 which are normally pressed between contact pairs 28 and 30. Contact pairs 28 and 30 are connected to the electrode hoist mechanism 32.

A second differential relay 34 includes contacts 36 and 38 which are connected respectively to armatures 24 and 26 of relay 22. Relay 34 further includes an armature 40 which is normally in a neutral position, i.e., not in contact with either of contacts 36 or 38, and coils 42 and 44. A double-pole, double-throw switch 46 enables coil 44 to be connected either across secondary winding 16 of power transformer l12- in series with a variable. resistance 48 as shown, or, when constant furnace current is d sired, across a constant reference voltage. Coil 42 is connected across a current-sensing coil S0, which detects the current flowing in the primary winding 14 of power transformer 12, Current-sensing coil 50 is shunted by a variafble resistance 52 to enable adjustment of the current through coil 42. Armature 40 of the differential relay 34 is connected to one of the power input terminals for the electrode hoist mechanism 32.

|In operation, power is applied across the primary winding 14 of power transformer 12 to produce a relatively low voltage-high current output in the secondary winding 16. Current flows between electrode 1 and the furnace bottom 10 and between electrode 2 and the furnace bottom '10, the paths of these currents -being through the charge 6 and the melt 8. When the potential between electrode 1 and the furnace bottom 10 does not differ from the potential between electrode 2 and the f-urnace bottom 10 fby more than a predetermined amount, differential relay 22 will not be actuated, i.e., the net flux produced 'by the currents through coils 18 and 20 will not be sufficient to attract armature 24, which is ganged with armature 26. Thus, if armature 40V of differential relay 34 should be drawn against contact 38V as a result of decreased furnace current causing increased voltage output across secondary winding 16, then power would 'be applied to the electrode hoist mechanism 32 through armature 40 and contact 38 of relay 34 and through armature 26 and both contacts of contact pair 30 of relay 32 to lower both electrodes '1 and 2 in order to increase furnace current. If furnace current should be too high, thereby causing a decreased voltage output across secondary winding 16, then armature 40` of relay 34 will be drawn against contact 36, and power will be applied to the hoist mechanism 32 through armature 40 and contact 36 of relay 34 and through armature 24 and both contacts of contact pair 28 of relay 22 to raise both electrodes 1 and 2 in order to decrease furnace current.

It might happen that electrode 1 is immersed more deeply in the charge -6 than electrode 2, thus causing the current and the potential between electrode 1 and the furnace bottom 10 to exceed the current and the potential between electrode 2 and the furnace bottom 10. If these two potentials differ by a sufficiently large increment, the flux produced by coil 18 of relay 22 will be lessened to a level at which armature 24 will be drawn toward coil 20, thus breaking the contact between armature 24 and the left contact of contact pair 28 while maintaining contact with the right contact. Similarly, ganged armature 26 will break contact with the left contact of contact pair 30 while maintaining contact with the right contact. Thus, when armature 40 of relay 34 is drawn against contact 36 as a result of the increased furnace current, power will be applied only to that portion of the hoist mechanism 32 which operates to raise electrode 1. Power will be applied to the hoist mechanism 32 through armature 40 and contact 36 of relay 34 and through armature 24 and the right contact of contact pair 23 of relay 22 to effect the adjustment of the position of electrode 1 only. If it is electrode 2 that is immersed too deeply in charge 6, a similar adjustment would be made for this electrode by movement of the armatures 24 and 26 leftward so as to break contact with the right contacts of contact pair 28 and 30 while maintaining contact with the left contacts. If either or both electrodes 1 and 2 are not immersed far enough into the charge 6, armature 40 of relay 34 will be drawn against contact 38 as a consequence of the decrease in furnace current and the resultant increase in voltage across the secondary winding 16 of transformer 12.

FIG. 2 schematically illustrates one possible form of the hoist apparatus 32. Specifically, this ligure illustrates an electromagnetic type of hoist apparatus, which, when connected into the circuit of FIG. l, as shown therein, will serve to raise or lower both of the electrodes 1 and 2 or a selected one of the electrode pair. This hoist apparatus consists of a first pair of windings 54 and 56 associated with a moveable magnetic core 58 which is mechanically connected to electrode 1; and a second pair of lwindings 60 and 62 associated with a moveable magnetic core 64 which is mechanically connected to electrode 2. Winding 54 is connected in series between the left contact of contact pair 28 and ground; winding 56 is connected in series between the left contact of contact pair 30 and ground; winding 60 is connected in series between the right contact of contact pair 28 and ground; and winding 62 is connected in series between the right contact of contact pair 30 and ground. Thus, when armature 40 of relay 34 is urged against contact 36 as a result of increased furnace current, each of the windings 54 and 60 will be energized through armature 24 of relay 22 and contact pair 28 and the moveable cores 58 and 64 will be drawn upward, thus raising both electrodes 1 and 2` to decrease furnace current. This assumes, of course, that the difference between the potentials between the furnace bottom 10 and the electrodes 1 and 2 is not above the predetermined threshold value which will actuate relay 22, thus causing only the electrode conducting the most current to be raised.

Similarly, if armature 40 of relay 34 is urged against contact 38 as a result of decreased furnace current, then windings S6 and 62 will be energized through armature 26 and contact pair 30 of relay 22, thereby urging the moveable cores 58 and 64 downward and thus lowering electrodes 1 and 2 in order to increase furnace current. Again, if there should be a sufliciently large difference between the electrode-to-oor potentials, only the electrode carrying the lightest current will be lowered.

Although the present Vinvention is primarily concerned with electrical reduction furnaces in which the resistant medium is formed by a charge introduced into the furnace, it Should be understood that the invention has applications in other fields. For example, it could be utilized in electric boilers. Also, the present invention may be employed with either an alternating current powered furnace or a direct current powered furnace. Various equivalents of the control circuit components will be obvious to one knowledgable in the art.

The advantages of the present invention, as well as certain changes and modifications to the disclosed embodiment thereof, will be readily apparent to those skilled in the art. It is the applicants intention to cover all those changes and modifications which could be made to the embodiment of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.

What I claim is:

1. An automatically-controlled electric smelting furnace system comprising:

(l) an electric furnace having at least one pair of electrodes;

(2) means for applying electric potential between the bottom of said electric furnace and each of said at least one pair of electrodes;

(3) hoist means for adjusting the position of said at least one pair of electrodes or of either one of said at least one pair of electrodes;

(4) relay means responsive to a predetermined minimum difference between the potentials between the bottom of said furnace and each of said at least one pair of electrodes to enable said hoist means to adjust only a selected one of said at least one pair of electrodes, and responsive to a difference between said potentials less than said predetermined minimum difference to enable said hoist means to adjust both of said at least one pair of electrodes; and

(5) means responsive to uctuation in furnace current to provide to said hoist means through said relay means an input which causes said hoist means to adjust the positions of said at least one pair of electrodes or of a selected one of said at least one pair of electrodes so as to stabilize the value of furnace current.

2. The furnace system according to claim 1 wherein said means for applying electric potential is a transformer having a core and primary and secondary windings, said at least one pair of electrodes being connected in series with said secondary winding and with each other.

3. The furnace system according to claim 2 wherein said means responsive to fluctuations in furnace current comprises:

(l) a differential relay having an armature connected to one power input terminal of said hoist means, iirst and second normally-open contacts, and first and second coils;

(2) a current-sensing coil for sensing primary winding current in said transformer, and a variable resistance for shunting a portion of the output current of said sensing coil, said first coil of said differential relay being connected across said current-sensing coil; and

(3) switching means for selectively connecting said second coil of said differential relay either in series with a variable resistance across said secondary winding of said transformer or across a constant reference voltage source.

4. The furnace system according to claim 3 wherein said relay means responsive to differences in the potentials from the electrodes to the furnace bottom comprises first and second ganged armatures, a pair of normallyclosed contacts associated with each of said armatures, and iirst and second coils associated with at least one of said armatures, said first and second armatures being electrically connected respectively to said iirst and second contacts of said differential relay of said means responsive to fluctuations in furnace current, said contact pairs being electrically connected to said hoist means, and said rst and second coils being connected across said furnace bottom and the rst and second electrodes, respectively, of said at least one pair of electrodes.

5. The furnace system according to claim 4 wherein said hoist means comprises:

(l) rst and second windings and an associated movable core which is mechanically connected to said rst electrode, said first and second windings being operative when energized to move said movable core upwardly and downwardly, respectively;

(2) third and fourth windings and an associated movable core which is mechanically connected to said second electrode, said third and fourth windings being operative when energized to move said movable core upwardly and downwardly, respectively.

References Cited UNITED STATES PATENTS 10/1955 Jordan 13-13 X 4/1968 Bobo 13-13 

